Francesco Pecoraro, Associated Press - ApRescue personnel stand on rubble next to a tilted staircase, part of a control tower which collapsed after a cargo ship slammed into it during a shift change Tuesday night in the port of Genoa, northern Italy, killing at least five people, Wednesday, May 8, 2013. By Wednesday morning, all that was left of the control tower was the mangled exterior staircase, tilted to its side. The tower itself, which was located on the very edge of a dock jutting out into the harbor, was either in the water or in a heap of wreckage on the dock.

ROME - Italian prosecutors placed the captain of the Jolly Nero cargo ship under investigation Wednesday for alleged manslaughter after his vessel slammed into the dock at Genoa's busy port and toppled the control tower into the harbor, killing at least seven people.

As rescue teams in diving suits searched for two other missing people, officials began piecing together how the 40,000-ton container ship could have sideswiped the port's control tower when weather and sea conditions were "perfect" on Tuesday night. The focus was on whether human error or a technical malfunction was to blame.

The crash occurred around 11 p.m. as the Jolly Nero was backing out of Genoa's port accompanied by two tugboats and with a harbor pilot on its bridge. At the same time, a shift change was taking place among employees at the control tower, meaning more people were in the building than usual.

"This event is unbelievable because we had the best weather navigation conditions," said Luigi Merlo, president of Genoa's port authority.

Transport Minister Maurizio Lupi told Parliament that given the "perfect" weather conditions, possible causes of the crash could include an engine malfunction or problems with the cables between the container ship and the tugs guiding it. He said investigators — both criminal and from his own ministry — were also looking into possible mistakes with the maneuver itself or with the speed in which the ship backed out of its berth and turned around to leave the port.

The Jolly Nero's captain, Roberto Paoloni, and the harbor pilot on board were placed under investigation for alleged manslaughter, Genoa prosecutor Michele di Lecce told reporters. He said other accusations were possible.

, Associated Press - Ap

This undated photo made available Wednesday, May 8, 2013, shows the control tower of the port of Genoa, northern Italy, that collapsed after a cargo ship slammed into it killing at least five people, late Tuesday, May 7, 2013. A cargo ship identified as the Jolly Nero of the Ignazio Messina & C. SpA Italian shipping line slammed into the port.

Such an investigation is par for the course in Italy.

Lecce said backing out of the port was a frequently used maneuver to get away from the dock.

"Now we have to understand if it was done correctly," he told reporters. "If it was done according to the way it was supposed to, or if something wasn't respected or if something didn't work. It could be an issue that concerns behavior — so a human issue — or a technical problem."

Firefighter spokesman Luca Cari confirmed that seven people were killed, saying rescue crews recovered several bodies near the tower's submerged elevator. There were fears the two still missing might be trapped inside the elevator, he said.

The dead included three coast guard officials in the tower at the time of the crash, a port captain and a tugboat operator, said Cmdr. Filippo Marini, a coast guard spokesman.

Four other people were injured. There were no reports of missing ship crew members.

The Jolly Nero, which belongs to the Genoa-based Ignazio Messina & C. SpA Italian shipping line, is 239 meters (784 feet) long and 30 meters (98 feet) wide, according to the company's website. It is one of Messina's 14 cargo ships.

Merlo declined to speculate on a cause, saying the ship had plenty of room to maneuver in the harbor and shouldn't have ended up so close to the dock. He said the Nero was an unusually high ship so its full weight slammed "violently" into the tower itself, not just the dock.

"The ship directly hit the control tower," he told Sky TG24.

In a statement, Messina said it was fully cooperating with authorities to determine the cause of the "tragic" accident, which it said took place during a normal maneuver to leave the port. It said Messina Line ships perform the maneuver often and are always accompanied by tugboats.

"There aren't words to express the dismay and our profound condolences for the victims of this tragedy and their families," the company said.

Andrea Furgani, a doctor who was one of the first rescuers, said crews brought four injured people in critical condition to hospitals in Genoa.

"They mainly suffered wounds caused by compression, broken bones and wounds on the chest," he told The Associated Press.

The disaster shook a nation that only a year ago witnessed another shipping tragedy when the Costa Concordia cruise ship slammed into a reef off Tuscany on Jan. 13, 2012, killing 32 people.

Parliament held a minute of silence Wednesday for the victims in Genoa, the mayor of Genoa proclaimed a period of mourning and Italian President Giorgio Napolitano sent condolences to the victims' families on behalf of the nation.

Genoa's port, located on Italy's western Ligurian coast, is Italy's busiest in terms of cargo handling, according to the port authority website. It is also a major port of call for cruise ships sailing the Mediterranean.

The control tower contained the radar and radio equipment that the Genoa port uses to communicate with incoming and outgoing vessels. With that equipment knocked out, the nearby port of Savona took over communications, ensuring that maritime traffic in Genoa continued almost unaffected Wednesday, Savona port Cmdr. Enrico Moretti told the AP.

He said about 20 ships move in and out of Genoa's port each day. He expected that Savona, about 34 miles (55 kilometers) to the west, would handle Genoa's communications for the next two weeks or so until its ship traffic control system is restored.

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